1. Field of the Invention
The present invention relates generally to inkjet printers and, in particular, to a method and structure for wiping the printheads of one or more print cartridges.
2. Description of Related Art
Inkjet printhead nozzles must occasionally be cleaned to remove ink residue or particulates from the nozzles; otherwise the nozzles would become clogged. Conventional service mechanisms in prior art inkjet printers typically provide wiping and capping of printheads to keep the nozzles from becoming clogged.
FIG. 1 illustrates one type of print cartridge 10 having a printhead which requires wiping after a printing session to avoid ink clogging the nozzles. Inkjet print cartridge 10 includes an ink reservoir 12 and a printhead 14, where printhead 14 includes a metal or plastic nozzle plate 16 having formed in it two parallel columns of offset nozzles 17. Nozzle plate 16 is affixed to the surface of a semiconductor substrate (not shown) having heater resistors and vaporization chambers formed on its surface which are aligned with each of the nozzles 17 formed in nozzle plate 16.
A flexible polymer tape 18 has conductive traces formed thereon which terminate in contact pads 20 for contacting corresponding electrodes on a printer when print cartridge 10 is installed in the printer. The conductive traces on tape 18 lead to a rectangular opening in tape 18 in which the nozzle plate 16 is located. The ends of the traces are bonded to exposed electrodes on the rectangular substrate underlying nozzle plate 16. After bonding the traces to the electrodes on the substrate, the electrodes and traces are exposed through the rectangular opening in tape 18 and must be protected from ink and physical damage. To provide such protection, adhesive beads 22 and 23 are dispensed over the exposed traces to encapsulate the traces. The adhesive may be epoxy or any other suitable adhesive.
In another embodiment of a print cartridge which may benefit from the present invention, a nozzle member is created by forming nozzles directly in tape 18 so no separate nozzle plate exists. Openings at both ends of the nozzle array still must be formed in tape 18 to allow the attachment of the conductive traces to electrodes on a substrate affixed to the back of tape 18. The adhesive beads 22 and 23 would still be required to encapsulate the traces.
FIG. 2a illustrates print cartridge 10, along with similar print cartridges 25, 26, and 27, installed in a slidable carriage 30 within an inkjet printer.
The snout portion 32 of print cartridge 10 in FIG. 1 is shown protruding through carriage 30 in FIG. 2a to be proximate to paper sheet 34.
Carriage 30 is moved along stationary rod 36 in the direction shown by arrow 38. A roller 40 shifts the position of paper sheet 34 as needed. In an actual embodiment, at least two spaced rollers are used to cause paper sheet 34 to be flat along where print cartridges 10 and 25-27 are scanned for printing.
In order to wipe nozzle plate 16 (FIG. 1) clean after a printing session, carriage 30 is automatically moved along rod 36 to a service station area 42. As carriage 30 is shifted into position into service station 42, a series of flexible rubber wipers 44 are raised into their wiping positions so that, as a print cartridge is moved past its associated wiper 44, a wiper 44 presses against the nozzle plate 16 of the associated print cartridge to wipe off residual ink.
Once carriage 30 has been fully shifted into service station 42, the printheads are capped to prevent the drying of ink and to prevent air bubbles from forming in the printhead. The capping function of an inkjet printer and the mechanisms used to raise wipers 44 into position to wipe the nozzle plates of the print cartridges are described in the co-pending applications and patents identified in the Cross-Reference to Related Applications.
Each of wipers 44 consists of a rubber, plastic, composite, or otherwise flexible single wiper blade. With certain types of print cartridges and printheads, the wipers 44 shown in FIG. 2a may be satisfactory for wiping a nozzle plate. However, for print cartridges similiar to the print cartridge 10 of FIG. 1, the raised adhesive beads 22 and 23 lift up an end of a wiper 44, as shown in FIG. 2b, if the wiper 44 is not properly aligned with respect to nozzle plate 16.
FIG. 2b is taken along line A--A in FIG. 1 to illustrate the effect of adhesive beads 22 and 23 on wiper 44 if wiper 44 is not properly aligned with respect to nozzle plate 16. Adhesive beads 22 and 23 may be approximately 1 mm wide and rise approximately 0.25 mm above nozzle plate 16.
FIG. 2b also illustrates semiconductor substrate 48 and illustrates conductive traces 50 on a back surface of tape 18 being bonded to electrodes 52 formed on substrate 48. A barrier layer 54 formed on substrate 48 defines vaporization chambers, where each vaporization chamber underlies a nozzle 17.
Adhesive beads 22 and 23 are shown encapsulating conductive traces 50 bonded to electrodes 52 on substrate 48.
If wiper 44 is misaligned slightly to the left of nozzle plate 16, as shown in FIG. 2b, bead 22 lifts up the end of wiper 44, leaving an unwiped portion of nozzle plate 16. If the end nozzles 17 are close enough to bead 22, then the lifting up of the end of wiper 44 will cause the end nozzles 17 to not be wiped.
To illustrate the required alignment tolerance of wiper 44, if beads 22 and 23 are located approximately 0.5 mm away from an end nozzle 17, then wiper 44 must be aligned within approximately 0.25 mm with respect to nozzle plate 16 to ensure the end nozzles 17 are correctly wiped. However, the practical consistent alignment of wiper 44 with respect to nozzle plate 16 is approximately .+-.0.5 mm. The molding tolerance alone for wiper 44 is .+-.0.2 mm. Hence, using the conventional wiper 44 to wipe nozzle plate 16 on print cartridge 10 in FIG. 1 will not work given the above alignment constraints.
What is needed is a new wiper design which can accommodate typical misalignments between a wiper and a nozzle plate without adversely affecting the wiping of the nozzle plate.